Synergistic antioxidant compositions



United States Patent 3,489,683 SYNERGISTIC ANTIOXIDANT COMPOSITIONS Robert E. Malec, Birmingham, Mich., assignor to Ethyl Corporation, New York, N.Y., a corporation of Virginia No Drawing. Filed May 29, 1967, Ser. No. 642,206 Int. Cl. (310m 3/20, 1/54, 3/32 US. Cl. 25246.4 11 Claims ABSTRACT OF THE DISCLOSURE Ester lubricants are stabilized against the effect of oxygen by the synergistic combination of a phenothiazine and a dihydrocarbyl tin sulfide. For example, the stabilizing effect of phenothiazine on di(2-ethylhexyl)sebacate is synergized by dibutyl tin sulfide.

BACKGROUND The stabilization of lubricants, especially ester type lubricants, with phenothiazine is known (R. C. Gunderson et al., Synthetic Lubricants, p. 193, Reinhold Publishing Company, New York (1962)). At elevated temperatures the quantity of stabilizer required results in sludging of the lubricant. Hence, a need exists to provide stabilization of lubricants with a reduced amount of phenothiazine that will not result in sludging.

SUMMARY An object of this invention is to provide lubricating oils of enhanced stability. A further object is to provide lubricants that can be used under adverse conditions such as elevated temperatures in the presence of oxygen for extended periods of time. A still further object is to provide an ester type lubricant especially useful in turbine engines.

These and other objects are accomplished by providing a synergistic stabilizer comprising from about to 99 weight percent of a phenothiazine and from 1 to about 90 weight percent of a dihydrocarbyl tin sulfide wherein the hydrocarbyl radicals contain from about 1 to 20 carbon atoms.

In a preferred embodiment the stabilizing composition comprises from about 75 to 99 weight percent of phenothiazine and from 1 to about 25 weight percent of the dihydrocarbyl tin sulfide.

Useful phenothiazines include both substituted phenothiazine and unsubstituted phenothiazine. These can be represented by the following formula:

R H R wherein each R is selected from the group consisting of hydrogen, alkyl groups containing 1 to 20 carbon atoms, aryl groups containing 6 to 20 carbon atoms, aralkyl radicals containing 7 to 20 carbon atoms, halogen and hydroxyl. Examples of suitable substituted phenothiazines are:

1,9-dimethyl phenothiazine 1,9-diethyl phenothiazine 3,7-diphenyl phenothiazine 1,9-diethyl-3,7-dichloro phenothiazine 3,7-dihydroxy phenothiazine 1-rnethyl-9-benzyl phenothiazine 3,7-dibromo phenothiazine 3,7-di-tert-butyl phenothiazine 3,7-dioctyl phenothiazine 1,3,7,9-tetramethyl phenothiazine The most preferred phenothiazine is phenothiazine itself.

The preferred dihydrocarbyl tin sulfides are those in which the hydrocarbon radicals contain from 1 to about 20 carbon atoms. Examples of these are dimethyl tin sulfide, diethyl tin sulfide, methylethyl tin sulfide, di(2- ethylbutyl) tin sulfide, di-n-dodecyl tin sulfide, dieicosyl tin sulfide, diphenyl tin sulfide, phenylbutyl tin sulfide, 3,5-di-sec-nonylphenyl tin sulfide, dibenzyl tin sulfide, benzyl butyl tin sulfide, ot-methyl-benzyl methyl tin sulfide, and the like. The more preferred dihydrocarbyl tin sulfides are dialkyl tin sulfides wherein the alkyl groups are lower alkyl groups containing from 1 to about 6 carbon atoms. The most preferred dihydrocarbyl tin sulfide is dibutyl tin sulfide.

The amount of the synergistic combination employed in lubricant compositions depends on the particular lubricant being stabilized, the use conditions, and the degree of stabilization required. All that is necessary is that an amount be employed such that satisfactory stabilization of the lubricant is obtained. In general, good results are obtained when from 0.01 to 5 weight percent phenothiazine and from 0.0005 to 0.5 weight percent dihydrocarbyl tin sulfide are presentin the lubricant. A more preferred use range is from about 0.1 to 3 weight percent of the phenothiazine and from about 0.001 to 0.3 Weight percent of the dihydrocarbyl tin sulfide. A most preferred concentration range in the lubricant is from about 0.2 to 1.0 weight percent of the phenothiazine and from about 0.005 to 0.1 weight percent of the dihydrocarbyl tin sulfide.

The synergistic stabilizers can be used in a Wide range of base lubricants such as petroleum-derived hydrocarbon lubricants and synthetic hydrocarbon lubricants such as polybutenes, ester lubricants, polyglycols, phosphate esters, silicones, silicate esters, fluoroesters, polyphenyl ethers, and the like. These base lubricants, their properties, and methods of preparation are adequately disclosed by Gunderson et al. in Synthetic Lubricants, Reinhold Publishing Company, New York (1962).

The petroleum-derived hydrocarbon lubricants include those of a wide viscosity range of from about SAE-S to SAE50. These lubricants can be prepared using any of the well-known refining methods such as solvent refining and can be of the aromatic, naphthenic or paraffinic type.

Synthetic hydrocarbon oils are those lubricants derived from the polymerization of low molecular Weight olefins such as propylene, butene, isobutene, pentenes, hexenes, octenes, and mixtures of such monomers. The polymerization can be brought about by the use of catalysts such as aluminum chloride. The polymer oils have a wide range of molecular weights and viscosities. For example, the polybutene oils have viscosities ranging from 40 to over 3,000 SUS at 210 R, which corresponds to molecular weights of from 300 to about 1500. The flash point of these polybutene oils varies from about 200 to 500 F. 5121? izheir pour points range from about -65 F. to about The polyglycol type lubricants are long chain linear polymers formed by the reaction of an aliphatic alcohol or a phenol with an epoxide material such as ethylene oxide, propylene oxide, butylene oxide, or the like. This class of lubricants contains repeating ether groups in the polymer chain which are generally terminated with a hydroxyl group. In some instances, the hydroxyl group is blocked by formation of an alkoxy end group or by esterification of the terminal hydroxy radical with an organic acid.

The phosphate esters are a class of lubricant materials Whose chief beneficial characteristic is their lack of flammability. The most important of these lubricants are the aryl esters of phosphoric acid, which have good lubricity, high film strength and are non-corrosive. Examples of "Ice such phosphate esters include tricresylphosphate, trixylylphosphate, and the like.

The silicone lubricants are polymeric materials containing the elements silicon and oxygen and organic groups. The backbone of the polymer contains repeating siliconoxygen units which can be represented by the formula:

R R R Ball stic. t \R L 1'.

wherein the R groups can be the same or different organic radicals such as methyl, ethyl, propyl, amyl, benzyl,

phenyl, and the like. The most important silicone lubricants are'those in which the R groups are the methyl radicalr The molecular weight of the silicone lubricants de-.

pends on the degree of polymerization and varies from about 162 to over 100,000. Some examples of silicone lubricants include dimethyl polysiloxanes, diethyl polysiloxanes, diamyl polysiloxanes, methyl ethyl polysiloxanes, methyl phenyl polysiloxanes, diphenyl polysiloxanes,

and di-p-chlorophenyl polysiloxanes.

Silicate esters include both the ortho-silicate esters and the dimer silicate esters. The ortho-silicate esters are materials having the formula:

SitOR) 4 wherein the R groups are the same or different organic radicals such as alkyl, aryl, or mixed alkyl-aryl. These may be substituted by such groups as chloro, nitro, fluoroalkoxy, thioalkoxy, and the like. The ortho-silicate esters are sometimes referred to as tetraalkoxy or tetraaryloxy silanes. However, the silanes contain carbon silicon bonds and the properties of the two types of lubricants are different. Dimer silicate esters are similar to the ortho-silicafes and have the structure:

(RO) Si-O--Si( OR) 3 wherein the R groups can be any organic radical which may be the same or different. Furthermore, as was the case with the ortho-silicate esters, these organic radicals may be substituted with a variety of common substituents. The dimer silicate esters are frequently referred to as hexaalkoxy or hexaaryloxy disiloXanes. Some examples of silicate ester lubricants include tetrapropoxy silane, dimethoxy dihexoxy silane, tri'butoxy phenoxy silane, hexamethoxy disiloxane, hexabutoxy disiloxane, trimethoxy tripropoxy disiloxane, tetra-2-ethylhexoxy silane, tetra-ptert-butylphenoxy silane, tetra-p-chloro phenoxy silane, and hexa-p-chloro phenoxy disiloxane.

Polyphenyl ethers are compounds in which aromatic groups are connected through oxygen bridges. The aromatic groups can be simple phenylene radicals or substituted phenylene radicals. For example, 2,6-dimethylphenol can be converted to a polyphenyl ether with repeating 2,6-dimethylphenylene groups bonded through oxygen atoms. This is accomplished by treatment of 2,6-dimethylphenol with oxygen in the presence of a cupric chlorideamine catalyst. Preferably, the repeating arylene groups are bridged at different positions such as the ortho, meta and para positions because this results in a lower melting lubricant. Some examples of polyphenyl ethers include bis(p-phenoxyphenyl)ether, bis(o-phenoxyphenyl) ether, phenoxyphenyl-p-phenoxyphenyl ether, bis(mix-phenoxyphenyl) ether, p-di(p-methylphenoxy)benzene, p-di(ptert-butylphenoxy)benzene, di-(p-chlorophenoxy)benzene, and p-di(p-methoxyphenoxy) benzene.

Fluoroester lubricants are esters of fluoro acids and fluoro alcohols. The fluoro acids include both perfluoro monoand di-carboxylic acids. Typical acids include nonafluoropentanoic acid, SH-octafluoropentanoic acid, and the like. Typical fluoro alcohols are 1H,1H-nonafluoro-1-pentanol, 1H,1H,5H-octafluoro-1-pentanol, and the like. These materials result in such esters as 1H,lH-nonafluoropentyl nonafiuoropentanoate, 1H,1H,5H octafluoropentyl-SH- octafluoropentanoate, and the like. Other fluoro esters 4 can be prepared by the esterificationof a fluoro alcohol with a non-fluoro organic acid or by the esterification of a non-fluoro alcohol with a fluoro acid employing catalysts such as p-toluene sulfonic acid.

A preferred embodiment of the present invention is a lubricant' composition which contains a substantial amount, in excessof 10 percent and preferably over 50 percent, of an ester type lubricant and a stabilizing amount of the synergistic combination of a phenothiazine and a dihydrocarbyl tin sulfide. This class of lubricants is especially benefited by the synergistic etfect of the dihydrocarbyl tin sulfide. Ester lubricants include all the synthetic lubricants which are esters of an organic acid and an alcohol. These may be simple esters of monobasic organic acids and monohydroxyl alcohols, esters of polybasic organic acids and monohydroxyl alcohols, esters of monobasic organic acids and polyhydroxyl alcohols, complex esters of polybasic organic acids bridged by polyhydroxyl alcohols or polyglycols having terminal ester groups derived from monohydroxyl alcohols and esters of polybasic acids and polyhydroxyl alcohols or polyglycols with monobasic organic acid ester groups in the terminal position. Various types of ester lubricants are set forth in Synthetic Lubricants, ibid., p. 151245 and p. 388-401. v

The following classification describes. the preferred types of ester lubricants. In the first class are esters having the formula:

I'l R1-C-OR2] wherein R is a hydrocarbon radical having valence n and containing from about 2 to about 17 carbon atoms, R is an alkyl radical containing from about 4 to 16 carbon atoms, and n is an integer from 1 to 3. Some examples of these are:

The most preferred esters are those of these acids formed from branched chain primary aliphatic alcohols containing from about 6 to 12 carbon atomsf Thernost highly preferred esters are dioctyl esters, especially di-2-ethylhexyl sabacate, di-2-ethylhexyl adipate andldi-Z-ethylhexyl azelate.

The next class of esters benefited by thisinvention are those having the formula:

wherein R is selectedfrom the group consisting of hydrocarbon radicals having valence m and containing from about 2 to carbon atoms and polyalkyleneoxy radicals wherein each alkylene radical contains from 2 to 3 carbon atoms, R is an alkyl radical containing from about 4 to 20 carbon atoms, and m is an integer from 2 to 4. These esters are exemplified by:

ethylene glycol divalerate propylene glycol dilaurate hexamethylene glycol dihexoate decamethylene glycol diarachidate neopentyl glycol dicaproate ethylene glycol dipelargonate diethylene glycol dipelargonate neopentyl glycol dipelargonate tripropylene glycol dipelargonate neopentyl glycol didecanoate neopentyl glycol dilaurate trimethylolpropane trivalerate trimethylolpropane trihexanoate trimethylolethane triheptanoate trimethylolethane trilaurate trimethylolbutane trivalerate trimethylolbutane triheptanoate trimethylolbutane trilaurate trimethylolhexane trivalerate trimethylolhexane divalerate heptanoate trirnethylolhexane dilaurate valerate pentaerythritol tetravalerate pentaerythritol tetralaurate pentaerythritol divalerate distearate pentaerythritol tetrahexanoate pentaerythritol tetraheptanoate Of the foregoing, the most preferred esters are those of trimethylolproane with fatty acids containing from 5 to about 12 carbon atoms such as trimethylolpropane trivalerate, trimethylolpropane tripelargonate, trimethylolpropane tridodecanoate and mixtures containing these ester groups.

Still another useful class of ester lubricants are glycolcentered complex esters having the formula:

(III) wherein R and R are alkyl radicals containing from about 4 to 16 carbon atoms, R; and R are divalent hydrocarbon radicals containing from about 2 to 16 carbon atoms, R is an alkylene radical containing from 2 to about 10 carbon atoms, 12 has an average value of from about 1 to 6, and q has an average value of from about 1 to 3. These lubricants find use where a high viscosity lubricant is desired. These esters are formed by reacting about one mole of an alkylene glycol or polyalkylene glycol with about 2 moles of a dibasic organic acid so that the major product formed is the half-ester of the dibasic organic acid in which two molecules of the dibasic organic acid are joined at one end together through the glycol or polyglycol molecule. Of course, some of the molecules will contain two or more dibasic acid units since both'the acid and the glycol are bi-functional. Likewise, some dibasic acid will remain unesterified. The result is a mixture of products such that the average value of q in the above Formula III varies from 1 to about 3. The terminal groups on each of the molecules is an acid group. To finish the ester these terminal groups are esterified with a mono-functional alcohol containing from about 4 to 16 carbon atoms. Due to the complex nature of these esters they are best illustrated by means of the following table, in which each of the units in the ester represented by Formula III is set forth for different typical products.

R5 and R5 R1 and R5 R9 p (avg.) q (avg.)

n0ctyl \CH2/2 4.5 1.5

nButyl \CH2/m CH CH2- 2 3 Cetyl \0112/7 \CH2/2 6 1 2-eth 1h H-- y exyl \O 2/8 \CH% 1 1.2

Another class of dibasic acid-centered complex esters related to the above consists of those having the formula:

0 0 R a I II II H ro- -(oR12),0-oRn-o(R13-0 s -o-Ru wherein R and R are alkyl radicals containing about 4 to 20 carbon atoms, R and R are alkylene radicals containing from 2 to about 10 carbon atoms, R is a divalent hydrocarbon radical containing from about 2 to 16 carbon atoms, r and s have an average value of from about 1 to 6, and t has an average value of from about 1 to 3.

These complex dibasic acid ester lubricants are prepared by reacting about one mole equivalent of a dibasic acid containing about 4 to 18 carbon atoms with 2 to 3 mole equivalents of a glycol or po yglycol wherein each repeating alkylene unit contains about 2 to 4 carbon atoms, forming a diester wherein each ester group is terminated by a hydroxyl radical. The ester formation is completed by reacting these terminal hydroxyl radicals with a monobasic fatty acid containing about 5 to 20 carbon atoms. As was the case with the glycol-centered complex ester of Formula III, the dibasic acid complex esters of Formula IV are best illustrated by the following table showing typical Formula IV units.

1 and 8 R10 and R11 R12 and R13 R14 1 (avg) n-Butyl CH (0H2) 4.5 1.0 n-Ootyl CHOH2 (OH2)4- 2 1.5

n-0ctadeeyl (CH2)4 -(CH2)1- 6 3 2-ethy1nonyl -(CH2)iu-' 2)is- 1 L2 The following examples illustrate the stabilizing compositions of this invention that are useful as additives to a variety of base lubricants. Percentages are on a weight basis.

Percent (1) Phenothiazine 50 Dibutyl tin sulfide 50 (2) Phenothiazine 99 Dibutyl tin sulfide 1 (3) Phenothiazine l0 Diethyl tin sulfide (4) Phenothiazine 75 Di-n-octyl tin sulfide 25 (5) 3,7-dioctyl phenothiazine 90 Diphenyl tin sulfide l0 (6) 3,7-di-tert-butyl phenothiazine 80 Dibenzyl tin sulfide 20 (7) 1,9-diethyl-3,7-dichloro phenothiazine Di-(Z-ethylhexyl) tin sulfide 5 (8) 1,3,7,9-tetra-methyl phenothiazine 99 'Di(2-ethyloctadecyl) tin sulfide 1 The following examples serve to illustrate typical base lubricants containing thesynergistic stabilizers.

of a high molecular weight alkenyl succinic anhydride with tetraethylenepentamine as a dispersant is added 0.5 weight percent of 3,7di(l-methylnonyl)phenothlazlne and 0.05 weight percent of dibutyl tin sulfide.

Example 2 To 1000 parts of a polybutenesynthetic-lubricant made by the aluminum chloride catalyzed polymerization --f isobutylene and having a viscosity equivalent to a SAE-30 oil is added one weight percent of 3-(1-methylpentadecyl) phenothiazine and 0.01 weight percent of diamyl tin sulfide.

Example 3 To 1000 parts of a butyl-terminated polypropylene glycol having an average molecular weight of about 750 is added 3 Weight'percent of 3,7-dioctyl phenothiazine and 0.3 weight percent of di(2-ethyloctyl) tin sulfide.

Example 4 To 1000 parts of triscresylphosphate are added 5 weight percent of 3,7-difluoro phenothiazine and 0.5 weight percent of dibenzyl tin sulfide.

Example 5 Example 7 To 1000 parts of m-phenoxyphenyl'p-phenoxyphenyl ether is added 0.2 weight percent of 3,7-di(2-methyloctyl) phenothiazine and 0.001 weight percent of dibutyl tin sulfide.

Example 8 To 1000 parts of 1H,1H,5H-octafluoropentyl 5H-octafluoropentanoate is added 0.01 weight percent of phenothiazine and 0.0005 weight percent of dibutyl tin sulfide.

Example 9 To 1000 parts of n-butyl pelargonate is added 0.5 weight percent of phenothiazine and 0.005 Weight percent of dibutyl tin sulfide.

Example 10 To 1000 parts of 1-methylnonadecyl butyrate is added 1 weight percent of 3,7-dioctyl phenothiazine and 0.05 weight percent of dimethyl tin sulfide.

Example 11 To 1000 parts of di(2-ethylhexy l)adipate is added 0.5 weight percent of phenothiazine and 0.05 weight percent of dibutyl tin sulfide.

Example 12 I To 1000 parts of di(2-ethylhexyl)sebacate is added 1 weight percent of phenothiazine and 0.005weight percent otdibutyl tin sulfide. v v r Example 13 To 1000 partsof di(2-ethylhexyl)azelate is'added 5 weight percent of phenothiazine and 0.1 weightpercent of dibutyl tin sulfide.

3 r V I Example 14 V l To I 1000 partsof 'tri(2-ethylhexyl)aconitate is added 0.2- weight percent of 3,7-dioctyl phenothiazine and 0.3 weight percent of diphenyl tin sulfide. r

7 Example 15 I To 1000 parts of hexamethyleneglycol dihexoate is added 0.8 weight percent of 3,7-dichloropl1enothiazine and 0.005 weight percent of diamyl tin sulfide. 1

Exam le 1 I 1 To 1000 parts of ethyleneglycol pelargonate is added 0.7 weight percent of phenothiazine and 0.01 weight percent of dibutyl tin sulfide.

Example 17 To 1000 parts of trimethylolpropane trivalerate is added 1 weight percent of phenothiazine and 0.007 weight percent of dibutyl tin sulfide. H I H Example 18 v v To 1000 parts of pentaeryth'ritol tetrapelargonate" is added 0.5 weight percent of phenothiazine and 0.05 Weight percent of dibutyl tin sulfide. Y

Examplel9 I To 1000 parts of a glycol-centered complex ester formed by the acid catalyzed esterification reaction of one mole equivalent of hexamethyleneglycol with two mole equivae lents of sebacic acid followed by esterification with two mole equivalents of 2-ethylhexanol is added l'weight percent of 3,7-di(l-methylnonyl)phenothiazine and'0.01 weight percent of diamyl tin sulfide.-

" Example 20 To 1000 parts of a poly'glycol-centeredcomplex ester formed by the acid catalyzed e'sterification reaction of one mole equivalent of tetraethyleneglycol with' 2 mole equivalents of azelaic acid followed by esterification of the terminal acid groups with 2 mole equivalents .of 2-ethylhexanol is added 0.5 weight percent of .phenothiazine and 0.005 weight percent of di-n-propyl tin sulfide.

Tests were conducted to demonstrate the synergistic effect of dihydrocarbyl tin sulfides on phenothiazine stabilizers. The test used was the Panel Coker Test. This test is described in Aeronautical Standards of the Departments of Navy and Air Force, Spec. M-IL-L 7808C, dated Nov. 2, 1955. In the test, di(Z-ethylhexyl) sebacate, a commonly used ester lubricant, was placed in a sump under an aluminum plate which was heated to 600.F. The lubricant was periodically splashed against the heated plate and allowed to drain back into the sump. The .oil was splashed for 5' seconds and drained for 55 seconds. This cycle was repeated over a 10 hour period. Following this, the aluminum plate was washed with hexanesand the weight gain determined. Any gain in weight is due to thermal and oxidative breakdown of the ester lubricant leaving a carbonaceousdeposit. The test was carried out with ,the unstabilized ester lubricant and with the-same ester lubricant containing various stabilizers and stabilizer combinations. The results obtained are shown in. the following table. I

Deposit As the aboveresults show, dibutyltin sulfide hadvery little effect on the stability of the lubricant. However, when used in an amount of only 0.01 weight percent in combination with 0.12 weight percent of phenothiazine only 8 mg. of deposit formed. This represents a deposit weight much less than that obtained using twice the amount of phenothiazine. Hence, the dihydrocarbyl tin sulfide has greatly enhanced the stabilizing'effect of phenothiazine even when used in extremely low concentrations.

I claim: i

1. A synergistic stablizer comprising from about 10 to 99 weight percent of a phenothiazine having the formula:

wherein each R is selected from the group consisting of hydrogen, alkyl groups containing 1 to 20 carbon atoms, aryl groups containing 6 to 20 carbon atoms, aralkyl radicals containing 7 to 20 carbon atoms, halogen and hydroxyl, and froml to about 90 weight percent of a dihydrocarbyl tin sulfide wherein each hydrocarbyl radical contains from 1 to about 20 carbon atoms.

2. The stabilizer of claim 1 comprising from about 75 to 99 weight percent of phenothiazine and from 1 to about 25 weight percent of said dihydrocarbyl tin sulfide.

3. The stabilizer of claim 2 wherein said dihydrocarbyl tin sulfide is dibutyl tin sulfide.

4. A stable lubricant composition comprising, as a major component, a synthetic ester base lubricant and, as a minor component, a stabilizing amount of a composition of claim 1.

5. The lubricant composition of claim 4 wherein said synthetic ester lubricant is selected from the group of compounds having the formulae:

Br -R2] wherein R is selected from the group consisting of hydrocarbon radicals having valence m and containing from about 2 to 10 carbon atoms and polyalkyleneoxy radicals wherein each alkylene radical contains from 2 to 3 carbon atoms, R, is an alkyl radical containing from about 4 to 20 carbon atoms, and m is an integer from 2 to 4;

O O 0 II I] ll o o 0 II I H II I II RmC(O-R12)i-OCR14C(Ri3O).CRu

L .l wherein R and R are alkyl radicals containing about 4 to 20 carbon atoms, R and R are alkylene radicals containing from 2 to about 10 carbon atoms, R is a divalent hydrocarbon radical containing from about 2 to 16 carbon atoms, r and s have an average value of from about 1 to 6, and t has an average value of from about 1 to 3.

6. The lubricating oil composition of claim 5 wherein said ester lubricant is a 0 alkyl sebacate.

7. The lubricating oil composition of claim 6 wherein said ester lubricant is a dioctyl sebacate.

8. The lubricating oil composition of claim 6 wherein said ester is di(2-ethylhexyl)sebacate.

9. The lubricant composition of claim 8 containing from 0.01 to 5 weight percent phenothiazine and from about 0.0005 to 0.5 weight percent dibutyl tin sulfide.

10. The lubricating oil composition of claim 5 wherein said ester lubricant is a C alkyl adipate.

11. The lubricating oil composition of claim 5 wherein said ester lubricant is a C azelate.

References Cited UNITED STATES PATENTS 6/1942 Lincoln 252-464 X 6/ 1962 Eickemeyer et al 252-47 FOREIGN PATENTS 907,664 10/1962 Great Britain.

US. Cl. X.R. 

